|Situation||Looking in Message Details, found in Logs, the delivery status often shows error codes explaining why a message shows as bounced or deferred.|
|Solution||These Error Codes can provide clues that can assist an admin in troubleshooting and correcting issues with their mail system.|
Any time you see the error This message was rejected by its destination for reasons outside the control of Proofpoint Essentials, and got returned to the sender, it means that this is outside our control, and this issue must be with the Customer/Recipient server accepting the message.
452 4.3.1 Insufficient system resources
This normally means that the recipient/customers server doesn’t have enough resources to accept messages. Customer/recipient needs to resolve this issue before we can deliver the message.
550 5.7.1 : Recipient address rejected
User email address is marked as invalid. This means normally you have SMTP Discovery enabled and the user is on the SMTP Discovery Invalid list. Remove this user from this list to resolve this issue.
550 5.1.0 sender rejected
The senders IP address is rejected due to a Blacklist/ wrong SPF. This is outside the control of Proofpoint Essentials
550 5.7.1 Relay Access denied
We are a closed relay system. This means if a user is in the Proofpoint Essentials system we will deny access to any e-mail that is not registered. More information on this error can be found here.
For more information and understanding on error codes please visit https://tools.ietf.org/html/rfc3463